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http://www.newscientist.com/news/news.jsp?id=ns99991891

Skis to get electronic brakes

Skis and snowboards could soon be fitted with built-in electronic brakes to slow them down before things get too terrifying for novices on the piste.

How electrical charges make skis sticky
The new system is being developed by Victor Petrenko, an engineer at Dartmouth College's Ice Research Lab in New Hampshire. His idea involves running a pair of wires the length of the board or ski's underside, one at each edge.

The wires are connected to opposite terminals of a three-volt battery, making one wire positive and the other negative. Fingers branching off the wires every few millimetres form an intersecting series of positive and negative electrodes covering the entire underside of the snowboard or ski.

The braking effect arises from a useful property of ice: it is a "dielectric" material that can hold a charge. When a positive electrode comes into contact with compact snow, it induces a negative charge at the surface; in the same way, the negative electrode induces a positive charge in the snow. Because opposite charges attract, this pulls the board closer to the snow and increases friction.

Sticky skis

And there's another effect that can help slow you down on snow and ice (see Graphic). Looked at under a microscope, the surface of snow is covered with a series of ultrafine icy ridges just a few micrometres high. When these ridges come into contact with two opposite electrodes on one of Petrenko's skis, a small current passes through the ice and melts it.

"The contact points are tiny and melt within a millisecond," says Petrenko. But once contact with the electrodes is broken, the water refreezes and sticks to the ski. The force required to break the bond between the ski and the ice helps to hold the skier back.

The brakes worked well in tests, says Petrenko. "The change in friction you get is equivalent to going from being on ice to dry pavement."

Speed limit

He is now working with a snowboard manufacturer and hopes that snowboards fitted with his brakes will be available in 2003. A sensor fitted to the boards will monitor the board's speed over the ice, and switch the brakes on if it's going too fast.

Petrenko expects his idea to find a ready market. In 2001, 11,000 Britons were injured skiing in France alone, and several died. And the French government has rushed through measures allowing it to ban dangerous, macho skiers and boarders.

Skis and snowboards aren't the only surfaces that need to get a grip on snow. Petrenko's next aim is to build shoes and car tyres incorporating similar electronic mechanisms.

Ian Sample